I have a 1991 RS camaro with a 305 tbi. I want to swap a 350 in it. My friend, the mechanic, said he can do it for me. He said he can install a 1990 block 350 using iroc specs, whatever that means, and use the 305 heads but change the pistons or something to that effect to make the heads compatible. He also said the valves on the 305 run alittle larger so it will actually increase the HP on the 350 using the 305 heads. Does any of this make since? Unfortunately I might not be wording this correctly because I am no mechanic. If this sounds authentic, should I go with it or just buy a crate 350? Any help appreciated. Cheers Sticky

 

The valves are smaller on a 305 head so it will make less horsepower.

The reason he would change the pistons is because the 305 heads have smaller combustion chambers so they generate a higher compression ratio.

I would recommend against the combo you are suggesting since the 305 heads you have are an incredibly inferior design for any RPM range of horsepower. I would buy a crate 350 instead, or better yet just get a 350 from a classifieds paper, rebuild it and choose your own heads.

 

Absolutely without question do not use the heads currently on your 305. Those are "swirl port" heads, which are fine for good gas mileage, but really stink for power - even on a 305. Put them on a 350, and it'll be weezing horribly.

A set of heads off of a TPI 305 would be a different story. They can be made to work decently on a 350.

What 305 heads do for you is raise the compression because of a smaller combustion chamber. However, you have to maintain flow through them to support the power the additional displacement of the 350 can provide, and to do that you should have larger intake valves (at least) put into the 305 heads. Some basic porting work on the 305 heads is also highly recommended.

What he meant by special pistons is using dished top versions so the compression doesn't go too high. I don't know what he means by "Iroc specs", unless that means a better cam than your TBI engine has.

Overall, though, like iroc22 says, you'd most likely be better off just getting a 350, out of a TPI car would be nice, and putting it in.

 

when i bought my firebird it had a 350 truck short block with 305 heads and a tbi on top. it was kinda fast but not fast enough to brag about probably ran a mid 14. i though the only diffrence between 305 and 350 heads is the port size and chamber cc.